Polyethylene powder as an adsorbent for complexing dyes: influence of dye structure, solvent, pH, and ionic strength

Abstract

The application of polyethylene (PE) powder to the adsorption of complexing dyes has been studied. Rhodamine B, aluminon, o-phenanthroline and dithizone were used as model substances of cationic, anionic, slightly polar, and apolar species, respectively. The influence of PE type, solvent, pH, and ionic strength on the adsorption was investigated. The results showed that high-density PE adsorbs polar dyes, preferentially cationic dyes, from aqueous solutions, whereas low-density PE adsorbs apolar dyes from an apolar milieu. The adsorption of polar species occurs probably at negatively charged sites on the PE surface, whereas the apolar ones occurs at the apolar parts of the surface. Presence of salts and pH influence the adsorption, mainly of anionic dyes; for these, the lower the pH the higher the adsorption, showing that the undissociated anionic dye is adsorbed. The adsorption in ethanolic solutions was very weak, probably because ethanol, differently from water, wets PE and therefore competes with the dyes for the active sites on the PE surface. Complexes formed by metallic ions and dyes are also adsorbed on PE showing that, for analytical purposes, metallic cations can be separated from their matrix solutions using adequate PE and conditions for the separation.

Keywords:

• Adsorption
• Dyes
• Polyethylene powder

Acknowledgments

The authors express their grateful thanks to the Brazilian organization CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) for financial support.